'We've found that pigs find even mild sorts of human behaviour offensive,' said Grahame Coleman, who is a psychologist at La Trobe University, Bundoora, Victoria.
Mr Coleman said the common farm practice of slapping and kicking the rumps of pigs when moving them between pens could cause chronic stress reactions similar to the build-up of tension in executives.
'While not painful, this treatment increases the animals' fear,' he was reported as saying.
'By contrast, a lot of positive physical contact, with friendly pats and strokes, eases stress and increases litter size,' he said.
Australian pig researchers, who have been examining the pig-human relationship for 13 years, have found that variations in output between farms can be partly explained by differences in the way farmers handle their pigs, said Mr Coleman. The Victorian Institute of Animal Science has been commissioned to design a 'pat-a-pig' programme for the Pig Research and Development Council.